And how much fretting do you do about where you kept that night light you put away years ago?

“Paranormal Activity 3″ manages a couple of hair-raising moments, a couple of legitimate jolts and some funny cheap ones. It was directed by the fellows who did that semi-legit documentary “Catfish,” so it’s more cinematic. Jump cuts and the occasional almost-movie-like arresting camera angle intrudes on the “found footage” this time — old VHS home movies from our pursued-by-demons sisters, Katie and Kristi, scenes from their childhood and their first brush with ghosts.

But this “Paranormal” doesn’t tamper with the formula that worked in the first two films. It lacks the “money” moments that those films delivered and ends with a finale that is downright conventional. “Paranormal” reveals itself for what it has become, the “Saw” of found video thrillers.

Katie (Katie Featherston) drops off some tapes with her sister (Sprague Graydon), and the sister’s house is trashed by the mere presence of VHS in an all-digital home. We’re taken back to the VHS world of the girls’ childhood — 1988– when sexy mom (Lauren Bittner) was shacking up with Dennis, the videographer (Christopher Nicholas Smith). Young Kristi (Jessica Tyler Brown) has an imaginary friend. When Dennis spies a shape outlined in the dust of a video taken during an earthquake, he rigs the house with cameras and starts to see the things that are going bump in the day. And night.

You know the drill, lots of “What was THAT?” and “Weird,” footage of lights swinging without a breeze, shadows, and sheets rising on their own. A consumer tip here — a great deal of what’s in the trailers to “Paranormal 3″ isn’t in the movie. So if you were thinking of suing over “Drive” being false-advertising, wait’ll your lawyer sees this.

The novelty here is that children are menaced. And their babysitter. Co-directors Henry Joost and Ariel Schulman find a lot more laughs in this situation, tossing in Randy (Dustin Ingram) as the comical slacker assistant videographer. They do well with the lull-us-into-complacency thing, endless shots of nothing –or what looks like nothing — happening. It makes you drop your guard.

They have a harder time maintaining the point of view shots, with Dennis obsessively shooting everything.They even have to address the simple physics of that. Where would he find the time to watch those hours of video? And the dialogue is banal to the point of “too real to be entertaining.”

But the kids, despite the absurdity of them sleeping through the night after having supernatural encounters, , are on the money — right down to the sibling teasing.

“Only babies have imaginary friends.”

Don’t think I’d be taunting the kid sister with that one, Katie. Not when the imaginary friend can shake the whole house if he’s irked.